1. Field of the Invention
The present invention relates to a semiconductor device and an insulating substrate for the same, and more particularly, to a semiconductor device and an insulating substrate for the same preventing breakdown caused by thermal stress to increase the product's life.
2. Description of the Related Art
An insulating substrate of a ceramic substrate having sheet-like metallic conductors on the both sides respectively is used for a power semiconductor device. A power semiconductor element of IGBT for instance is fixed on the metallic conductor on the front surface of the ceramic substrate by a solder layer. The metallic conductor on the back surface of the ceramic substrate is fixed on a metallic base board by a solder layer. As the thermal expansion coefficients of the ceramic substrate and the metallic base board which are connected by the solder layer are different from each other, cracks are generated in the solder layer when the temperature of the power semiconductor device changes. Correspondingly, for instance, the area of the metallic conductor fixed on the back surface of the ceramic substrate is made broader than that of the back surface of the ceramic board, so that the concentration of the thermal stress near the corner portions of the ceramic substrate is specially prevented, and the generation of the cracks in the solder layer is prevented (JP, 2000-349209, A).